An actuator used for operations, such as conveying, chucking, and fabricating a workpiece, is operated by energy, such as pneumatic or hydraulic pressure and electricity. Among them, an electric actuator using the electric energy, although it is excellent in optionally changing or adjusting the point of a force applied to the workpiece, has a complicated structure, and it has especially complicated structure for obtaining linear motion. In order to obtain a large action force, the increase cannot be avoided in size and electric power, and for maintaining a predetermined stop position, the electric power supply must be continued meanwhile, so that the energy loss is also increased. Furthermore, when an action force is added to the load via a rod, etc., an impact is directly applied to a power transmitting portion of the actuator, so that not only the actuator suffers mechanical damage but also an excessive repulsive force may be applied to the load.
On the other hand, as a pneumatic actuator, an air cylinder has been well-known. The air cylinder, which converts energy of compressed air into linear motion, includes a double-acting air cylinder, in which by alternately supplying air into air chambers formed on both sides of a piston, the piston is reciprocally moved; and a single-acting air cylinder, in which by air supplied to or exhausted from an air chamber formed on one side of a piston and an urging force of a spring arranged on the other side, the piston is reciprocally moved. Any of these types is widely used for various operations because the linear motion can be obtained more readily than in the electric actuator.
However, generally, the operation stroke of the air cylinder is mechanically determined so as to reciprocally move between positions of advance and retreat ends defined by stoppers, so that it is difficult to change or adjust the operation stroke (operation positions). In particular, it is difficult to optionally change or adjust the operation stroke. Therefore, in general, air cylinders with different strokes are properly used depending on operation kinds.